Larvae of the freeze-tolerant gall fly Eurosta solidaginis were sampled from outdoor populations over the course of a winter season and levels of cryoprotectants (glycerol, sorbitol), sugars, fuel reserves (glycogen, glycerides, protein), and lactate were monitored and correlated with the ambient temperature profile. Glycerol production was first stimulated in response to average daily temperatures of 10-15°C with highest rates of synthesis during early October when average temperatures were cooler and minimal daily temperatures did not exceed 8°C. Sorbitol production was initiated in mid-November in response to minimal daily temperatures below 3°C. Winter accumulations of cryoprotectants averaged 360 ± 27 and 119 ± 18 μmol/g wet weight for glycerol and sorbitol, respectively. Loss of cryoprotectants began first with sorbitol whose levels started to decline in February as maximal daily temperatures began to exceed 0°C. Loss of glycerol began in mid-March when average daily temperatures were well above 0°C but significant amounts (125 ± 23 μmol/g) still remained in pupae sampled in mid-April. During early autumn, larvae increased glycogen and protein content by 9- and 2-fold, respectively and increased total glyceride content by 50%. Glycogen was then rapidly depleted and quantitatively converted into polyols as autumn progressed. However lipid and protein reserves remained stable over the winter. Glycogen also appeared to be the fuel reserve supporting basal metabolic rate throughout the winter. During the spring, sorbitol pools were reconverted to glycogen stores but glycerol carbon was not. Lactate levels were fairly constant at 1-2 μmol/g in larvae over the winter suggesting that periods of freezing, necessitating anaerobic carbohydrate fermentation, did not produce a cumulative stress on larvae.

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Journal of Insect Physiology
Department of Biology

Storey, J, & Storey, K. (1986). Winter survival of the gall fly larva, Eurosta solidaginis: Profiles of fuel reserves and cryoprotectants in a natural population. Journal of Insect Physiology, 32(6), 549–556. doi:10.1016/0022-1910(86)90070-3